The enzymology of cholesterol formation from lanosterol in rat liver microsomes is under study. The approach has been to identify the enzymes while microsomal-bound then to solubilize and purify the released enzymes. To date, more than half of the 19-step process has been elucidated. After resolution of the enzymes from each other and from accompanying microsomal electron carriers the enzymes for catalysis of cholesterol formation will be reconstituted into an artificial phospholipid membrane. The studies include the roles of microsomal electron carriers in the biosynthetic process as well as regulations of rates of the microsomal enzymes. Ultimately, the enzymology should be described completely and a rational design of inhibitors of the enzymes designed for studies of pharmacological attenuations of cholesterol biosynthesis.